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Electrical Fires: Origins Common and Unique. Factory Mutual Engineering Corp. 1978.

Abstract: This article provides some statistics of electrical fires from 1965-1975. The statistics were compiled from Factory Mutual insured plants. During these ten years 3, 882 fires of electrical origin occurred. Fifty percent of the fires were a direct result of wiring and over seventy percent of the fires were caused by the top six electrical causes. The article summarizes these six most common electrical causes.

Wiring is the most common electrical cause of fires because they are connected to almost every part of the electrical system. Grouping wires together in steel enclosures or other similar devices is a common practice. This allows fires to advance before discovery and makes them harder to extinguish because they are inaccessible, which results in more property damage. To prevent wire fires, cables with non-combustible insulation or self-extinguishing cables should be used. Also, wires can be coated to prevent the spread of fires, but this must be done carefully so additional heat is not generated.

Electric motors that are maintained improperly or are not equipped with the proper electrical protection are the second greatest cause of electrical fires. The most common electric motor cause is overheating due to single-phasing. When a polyphase motor is operating without the proper overload relays, it can overheat and ignite when one phase becomes de-energized due to a fuse or the circuit breaker. Motors should be lubricated to the exact specifications because too little, as well as excess lubrication are both dangerous. Motors should be cleaned regularly because dirt can block air passages, allowing heat to build up. Synchronous motors should be maintained properly because there are many malfunctions that can cause overheating. Lightning surges also present a hazard because the sudden increase in voltage can cause the insulation to fail. To prevent this, lightning arresters should be installed close to the electrical equipment.

Electrical elements, mostly resistance grids and heating elements, rank third on the list of most common electrical fire causes. These fires occur because these elements are not installed or protected properly. Sometimes resistance grids are simply placed too close to combustible materials. Most heating elements overheat because the temperature controls are not accurate or they fail. The temperature controls of a heating device should be backed up with an excess temperature indication device.

Controllers and switches are also a common cause of fires when they are maintained improperly. Overheating and arcing will occur because contacts carrying current become dirty, loose, or corrode. Overcurrent protection for control centers is needed to prevent this from happening. Circuit breakers that control electric arc steel melting furnaces are subjected to extreme stress. In these instances, an air- circuit breaker should be used and maintained frequently.

Transformers fail frequently resulting in fires. Overloading, internal failures, and lightning are some of the reasons transformers fail. The oil-insulated transformer is the most popular because it is the most inexpensive; however, it the most dangerous because internal failure can cause the expulsion of burning oil resulting in massive damage. The national electrical code has specific regulations for the installation of both indoor and outdoor transformers.

Generators are the sixth most common electrical fire cause. To prevent oil-fire hazards, oil lines should be separated from steam lines and hot turbine parts. Hot, exposed parts should be insulated to prevent oil from coming in contact with them.

Most electrical fires are a result of minor defects that can be detected in the course of frequent maintenance. Proper protection and installation of electrical systems will also help prevent fires.

For more information, contact:
Factory Mutual Research Corporation
1151 Boston-Providence Turnpike
Norwood, MA 02139
Phone: (781) 762-4300

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